1. Field of Invention
The present invention relates generally to slant coil springs and, more particularly, to an improved slant coil spring which may be used to provide a substantially even load distribution in a seal.
2. Description of the Related Art
Seals including coil springs have been used to seal relatively reciprocating surfaces, such as those found in piston and cylinder arrangements and hydraulic rams, and relatively rotating surfaces, such as those found in rotating shaft and housing arrangements. Such seals are generally composed of an annular cup having a substantially U-shaped cross-section and an annular coil spring located within the cup. Typically, the cup is formed from a durable resilient elastomeric material. The coil spring forces the outer portion of the annular cup radially outwardly into engagement with the cylinder or housing and also forces the inner portion radially inwardly into engagement with the piston or rotating element. One example of this type of seal is disclosed in U.S. Pat. No. 3,223,426, which issued on Dec. 14, 1965.
Originally, these seals were provided with conventionally formed coil springs. The springs were deformed during assembly of the seal in such a manner that the individual coils were inclined at an angle relative to the axis of the spring, thereby preloading the spring and producing a radial force. Unfortunately, when coil springs were deformed in this manner, the pressure exerted by each individual coil could not be effectively controlled and the amount of distortion would vary. Thus, the action of the spring as a whole would not be uniform and the seal could not be used in applications which require a controlled and substantially uniform load over a wide range of deflection.
In an attempt to solve the problems associated with the preloading of coil springs, so-called slant coil springs were developed. Slant coil springs include coils having a portion which is inclined with respect to the spring's axis. Such springs tend to provide uniform and predictable load characteristics. One example of such a spring is disclosed in Patent Cooperation Treaty application No. PCT/US90/07682, which was published on Jul. 11, 1991.
While overcoming many of the problems associated with preloaded coil springs, prior art slant coil springs have presented a new set of problems, especially in the area of seals. In particular, individual coils in prior art slant coil springs form a steep angle of contact with the elastomeric material. This is especially true when prior art slant coil springs are bent into an annular shape for use in an annular seal. Here, a steep angle is formed between each individual coil and the inner and outer portions of the cup. As a result, the load generated by the spring is not evenly distributed over the resilient material. Rather, the load is imparted at a series of "points" with unloaded sections therebetween. The uneven load distribution and concentrated forces cause the resilient material to wear unevenly, which eventually reduces the integrity of the seal.